1. FIELD OF THE INVENTION
This invention relates to stable polymeric dispersant additives for lubricating oils which may also be useful as viscosity-index improvers for lubricating oils. More particularly, this invention relates to viscosity stable solutions of substantially saturated polymers comprising ethylene and one or more C.sub.3 to C.sub.28 alpha-olefins, preferably propylene, which have been grafted in the presence of a free radical initiator with an ethylenically-unsaturated dicarboxylic acid material preferably at an elevated temperature and in an inert atmosphere, and thereafter reacted first with a polyamine, preferably an alkylene polyamine, having at least two primary amino groups, such as diethylene triamine, and then with an anhydride of an organic acid, to form multifunctional polymeric reaction products characterized by viscosity stabilizing activity in mineral oil solutions.
2. DESCRIPTION OF THE PRIOR ART
Ashless dispersants or detergents for lubricating oil compositions are well known to enhance the sludge dispersing ability of said compositions.
One type of dispersant is generally derived from a hydrocarbon substituted dicarboxylic acid material such as an alkenyl succinic acid or anhydride reacted with a nitrogen-containing material. United Kingdom Patent Specification No. 1,018,982 teaches of reacting said alkenyl succinic anhydride with a 2-imidazoline or pyrimidine (the latter is obtained from the reaction of a carboxylic acid, e.g. acetic acid and an alkylene polyamine, e.g. diethylene triamine) to provide a sludge dispersant for lubricating oils. Similarly, U.S. Pat. No. 3,415,750 teaches of polyalkenyl succinicimido imidazolines and bis-imidazolines which can be used as said ashless detergents. The imidazoline is first prepared by the reaction of a polyethylene polyamine with a carboxylic acid or its anhydride, e.g. acetic which product is thereafter reacted with a polyalkenyl succinic anhydride.
In contrast to the above, U.S. Pat. No. 3,216,936 teaches that it is advantageous to insure that the reaction product of a mixture of a hydrocarbon-substituted succinic acid, a monocarboxylic acid and an alkylene polyamine does not come from an intermediate reaction product of said monocarboxylic acid and said amine in order to avoid destroying the sludge dispersant activity of the final reaction product.
It is well known that the introduction of carboxylic acid groups onto ethylene copolymers provides a means for derivatizing said copolymers which have viscosity index (V.I.) improving activity when dissolved in mineral oils. One means of introducing the carboxylic groups is by grafting of maleic anhydride onto said polymer as by a free radical mechanism.
Belgian Pat. No. 843,360 teaches the production of soluble, sludge-dispersing additives for hydrocarbon fuels and lubricating oils by the free-radical induced grafting in solution of an ethylenically-unsaturated dicarboxylic acid material such as maleic anhydride onto a substantially saturated copolymer comprising ethylene and at least one other alpha-olefin at an elevated temperature to provide, without substantial polymer degradation, a useful precursor copolymer which can be subsequently reacted with a carboxylic acid reacting polyfunctional material, such as a polyamine or a hydroxyamine or mixtures of these, to form multifunctional polymeric imidated derivatives having particular utility as engine sludge and varnish control additives for lubricating oils.
It is often found that during the storage of oil solutions of these various imidated grafted hydrocarbon polymers that the viscosity of the solution is increased. The source of this increase appears to be at least in part the chain extension of the polymer.
It is an object of this invention to provide a grafted ethylene copolymeric dispersant, generally useful as a mineral oil viscosity index improver of useful sludge performance and enhanced viscosity stabilizing activity.